This invention relates to a field emission cold-cathode device to be employed for a vacuum micro-device, etc. and also to a method of manufacturing the cold-cathode device.
Recently, the development of field emission cold-cathode device through a utilization of semiconductor processing techniques has been intensively studied. Typical example of which is the one proposed by C. A. Spindt et al., (Journal of Applied Physics, Vol. 47, 5248 (1976)). This field emission cold-cathode device can be manufactured by the steps of forming an SiO.sub.2 layer and a gate electrode layer on an Si monocrystalline substrate, forming a hole having a diameter of about 1.5 .mu.m, and forming, by means of vapor deposition, a conical emitter in the hole for actuating a field emission. This manufacturing method will be explained more in detail by referring to FIGS. 7A to 7C.
First of all, an SiO.sub.2 layer is formed as an insulating layer on an Si monocrystalline substrate 101. Then, a Mo layer 103 to be formed into a gate electrode layer and an Al layer 104 to be used as a sacrifice layer are formed on the SiO.sub.2 layer by means of sputtering method for instance. Thereafter, an etching is performed to form a hole 105 having a diameter of about 1.5 .mu.m and passing through the layers 102, 103 and 104 (FIG. 7A).
Then, an emitter 107 which is conical in shape for actuating a field emission is formed in the hole 105 by means of vapor deposition (FIG. 7B). The formation of this emitter 107 is performed by vacuum-depositing a material for the emitter such as Mo from the direction perpendicular to the substrate 101 while rotating the substrate 101. On this occasion, the opening size of pin-hole which corresponds to the opening size of the hole 105 is gradually decreased as the deposition of Mo layer 106 on the Al layer 104 increases, and ultimately becomes zero. Accordingly, the diameter of top surface of the emitter 107 being deposited in the hole 105 through this pin-hole becomes increasingly small in proportion to a decrease in size of the pin-hole, thus forming an emitter of conical shape. The superfluous portion of the Mo layer 106 deposited on the Al layer 104 is subsequently removed (FIG. 7C).
However, the aforementioned method as well as the field emission cold-cathode device obtained by the aforementioned method is accompanied with the following problems.
First of all, since the emitter is formed by taking advantage of the phenomenon that the diameter of the pin-hole which corresponds to the opening size of the hole 105 becomes gradually smaller in the rotational vapor deposition method, the height and shape of the emitter become non-uniform, thus deteriorating the uniformity in field emission of the emitter. Furthermore, since the reproducibility of the shape and the yield of well-shaped emitter become poor as a result, it will lead to a great increase in cost when a large number of the field emission cold-cathode devices having an excellent uniformity in quality are to be formed on a single substrate.
Additionally, since it is difficult according to the aforementioned conventional method to form a sufficiently sharp distal tip portion of the emitter which is required for improving the efficiency of field emission, not only the efficiency of field emission is deteriorated but also the power consumption by the emitter would be increased. When a high driving voltage is employed, the shape of the tip portion of emitter tends to be deformed by an influence from ionized residual gas generated by this high voltage, thus giving rise to problems of deterioration in reliability and life of the product.